Rotary drill bit shank, rotary drill bits so equipped, and methods of manufacture

ABSTRACT

A shank configuration for rotary drill bits, is disclosed for positioning of the shank in relation to the bit body. A tapered surface or feature of the shank may be configured and sized to matingly engage a complementarily shaped surface or feature of the drill bit body and thereby become centered or positioned in relation thereto. A deformable element may be disposed between the shank and bit body. Also, the shank may comprise a material having a carbon equivalent of less than about 0.35%. A multi-pass weld procedure may be employed to affix the shank and bit body to one another wherein welds may be formed so that one weld originates at a circumferential position that differs from the origination circumferential position of its immediately preceding weld by at least about 90°. Further, a stress state may be developed within the multi-pass weld. A method of manufacture is also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a drill bit shank for rotarydrill bits for drilling subterranean formations and to rotary drill bitsso equipped.

2. State of the Art

A typical rotary drill bit includes a bit body secured to a hardenedsteel shank having a threaded pin connection for attaching the bit to adrill string, and a crown including a face region carrying cuttingstructures for cutting into an earth formation. Generally, if the bit isa fixed-cutter or so-called “drag” bit or drill bit, the cuttingstructures include a plurality of cutting elements formed at least inpart of a superabrasive material, such as polycrystalline diamond.Rotary drag bits employing polycrystalline diamond compact (PDC) cuttershave been employed for several decades. Typically, the bit body may beformed of steel, or a matrix of hard particulate material such astungsten carbide (WC) infiltrated with a binder, generally of a copperalloy.

In the case of steel body drill bits, the bit body may typically bemachined from round stock to a desired shape. Radially andlongitudinally extending blades, internal watercourses for delivery ofdrilling fluid to the bit face, and topographical features defined atprecise locations on the bit face may be machined into the bit bodyusing a computer-controlled, multi-axis machine tool. Hard-facing forresisting abrasion during drilling is usually applied to the bit faceand to other critical areas of the bit exterior, and cutting elementsare secured to the blades on the bit face, generally by inserting theproximal ends thereof into cutting element pockets machined therein.After machining and hardfacing, the bit body may be secured to ahardened steel shank having a threaded pin connection for securing thesteel body rotary drill bit to the drive shaft of a downhole motor ordirectly to drill collars at the distal end of a drill string rotated atthe surface by a rotary table or top drive.

Matrix-type drill bits, on the other hand, include a bit body formed ofa matrix of hard particulate material such as tungsten carbide containedwithin a graphite mold and infiltrated with a binder, generally of acopper alloy. Cast resin-coated sand, graphite displacements or, in someinstance, tungsten carbide particles in a flexible polymeric binder, maybe employed to define internal watercourses and passages for delivery ofdrilling fluid to the bit face, cutting element sockets or pockets,ridges, lands, nozzle apertures, junk slots and other externaltopographic features of the matrix-type rotary drag bit. However,because a matrix material comprising tungsten carbide or otherrelatively hard particles may be substantially unmachinable, amachinable steel blank is typically disposed within the bit mold priorto infiltration of the matrix material, the steel blank forming aportion of the matrix-type rotary drag bit body upon hardening of theinfiltrant that affixes the blank therein. In a manner similar tofabrication of steel body drill bits, the matrix-type bit body, via themachinable blank, may be secured to a hardened steel shank having athreaded pin connection for securing the bit to the drive shaft of adownhole motor or directly to drill collars at the distal end of a drillstring rotated at the surface by a rotary table or top drive.

Thus, in either steel body or matrix-type rotary drill bits, alignmentbetween the bit body and the hardened shank is critical because theshank, which includes the threaded pin connection, may determine theaxis of rotation of the bit. Alignment of the axis of rotation inrelation to the cutting element design is obviously of great importancein the operation of a rotary drag bit because aspects of the rotarydrill bit design may be based, at least in part, on cutting elementpositions as well as predicted forces thereon. For instance, so-called“anti-whirl” designs utilize a preferential lateral force directedtoward a pad designed to ride against the formation in order tostabilize the rotary drag bit. Conventionally, a threaded connection hasbeen employed between matrix-type bit bodies and the hardened shank, asdescribed in more detail hereinbelow.

FIGS. 1A and 1B illustrate a conventional matrix-type drill bit 10formed generally according to the description above. Conventionalmatrix-type drill bit 10 includes a central longitudinal axis 3 and bore12 therethrough for communicating drilling fluid to the face of the bitduring drilling operation. Cutting elements 5 and 7 (typically diamond,and most often a synthetic polycrystalline diamond compact or PDC) maybe bonded to the bit face during infiltration of the bit body ifthermally stable PDC'S, commonly termed TSP's are employed, or may besubsequently bonded thereto, as by brazing, adhesive bonding, ormechanical affixation.

The conventional preformed, so-called blank 14 comprising relativelyductile steel may also provide internal reinforcement of the bit bodymatrix 19. The blank 14 may be typically comprised of relatively ductilesteel because the high temperatures experienced by the blank duringinfiltration may generally anneal most steel materials. Blank 14 maycomprise a cylindrical or tubular shape, or may be fairly complex inconfiguration and include protrusions corresponding to blades, wings orother features on the bit face. The protrusions or fingers may begenerally welded into longitudinal slots formed within the tubularportion of blank 14. The blank 14 and other preforms as mentioned abovemay be placed at appropriate locations within the graphite mold used tocast the bit body. The blank 14 may be affixed to the bit body matrix 19upon cooling of the bit body after infiltration of the tungsten carbidewith the binder in a furnace, and the other preforms are removed oncethe matrix has cooled. Blank 14 may be machined and affixed to shank 16by way of threaded connection 15 as well as weld 20. Conventionally, acontinuous weld may be formed between shank 16 and blank 14. The shank16 typically is formed from an AISI 4140 steel, a material having acarbon equivalent of higher than about 0.35%, which requires the shank16 and blank 14 to be preheated prior to welding. Shank 16 includestapered threads 17 machined at the upper portion thereof for connectingthe conventional matrix-type drill bit 10 to a string of drill pipe (notshown). Machined threads 17 are formed prior to attachment of the shank16 to the blank 14; therefore, proper alignment of the shank 16 with theblank 14 is critical.

FIG. 1C shows another conventional matrix-type drill bit 11 having aconventional shank 16 and illustrates the interface between the shank 16and bit body 23. Conventional matrix-type drill bit 11 includes aninternal bore 12 generally centered about the central longitudinal axis3 thereof. Shank 16 includes tapered threads 17 for attachment to adrill string (not shown) as well as “bit breaker” surface 21 forloosening and tightening the tapered thread connection between thematrix drill bit 11 and the drill string (not shown). Shank 16 may beaffixed to the bit body 23 by threaded connection 15 as well as weld 20.Of course, bit body 23 includes a blank (not shown) that provides theinterfacing surface between the bit body 23 and the shank 16.

FIG. 1D shows a conventional steel body drill bit 30 including bit body44 and internal bore 32 generally centered about central axis 33. AsFIG. 1D shows, conventional steel body rotary drill bit 30 includesshank 36 having a threaded connection 37 for connecting to a drillstring wherein the shank 36 is affixed by weld 40 to the bit body 44.Bit body 44 may also carry blade(s) 42 having cutting elements 38 forremoving formation during subterranean drilling.

As may be seen in FIGS. 1C and 1D, in manufacturing either a matrix-typeor steel body rotary drill bit, a shank is affixed to a bit body. Inaddition, in conventional welding of a shank to a bit body of a rotarydrill bit, the shank may comprise a material having a carbon equivalentof higher than about 0.35%, such as, for example, an AISI 4140 steel.Therefore, the shank and bit body may be preferably preheated to about700° Fahrenheit before welding begins. Further, conventional weldingprocedures may designate that as the shank is welded to the bit body, ifthe temperature of the shank reaches 90° Fahrenheit the weldingprocedure may be interrupted until the temperature is reduced. When theconventional weld procedure resumes subsequent to delay caused by eitheroverheating or inadequate heating of the shank, the weld may continuefrom substantially the same circumferential position as occurred atinitiation of the delay.

U.S. Pat. No. 6,116,360 discloses, in discussing a prior art steelbodied bit, a shank welded to a steel bit body that protrudes therein.However, the mating surfaces between the shank and the steel bit bodyare not tapered.

In addition, U.S. Pat. No. 5,150,636 to Hill discloses a shrink-fitbetween a cutting head and a shank. Further, Hill discloses that the tipof the shank may have a slight reverse taper to better retain thecutting head.

It has been observed by the inventors herein that the conventionalthreaded connection between the shank and blank may generate undesirablestresses within the threaded joint and proximate weld joint. Inaddition, the conventional threaded connection may produce misalignmentbetween the shank and bit body. Further, it has been observed that aconventional single-pass weld between the blank and shank may allow oreven promote distortion and misalignment therebetween. Thus, it would beadvantageous to eliminate the need for preheating of the shank prior towelding the shank to the bit body and a need exists for an improvedshank configuration for use in fabricating rotary drill bits.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a well-reasoned, practicallyimplementable shank configuration particularly suitable for rotary drillbits, which configuration may be tailored to a specific bit sizes andarrangements. In the inventive shank configuration, the shank maycomprise, a material having a carbon equivalent that is less than about0.35%, for example, an AISI 4130 steel or AISI 4130MOD steel. Such aconfiguration may enable elimination of preheating prior to welding thatis typically required by conventional shank materials, such as AISI 4140steel, and the presence invention contemplates and encompasses a methodof welding a shank structure to a portion of a bit body withoutpreheating of the shank structure.

Also according to the present invention, positioning of the shank inrelation to the bit body may be accomplished by engagement of taperedsurfaces thereof. For instance, a tapered surface or feature of theshank may be configured and sized to matingly engage a complementarilyshaped surface or feature of the drill bit body, such as on a portion ofa blank in the case of a matrix-type bit or any suitable portion of thebody in the case of a steel body bit, to become centered or positionedin relation thereto. The present invention is not limited to anyparticular tapered surface, since many arrangements may provide suchpositioning and more than one tapered surface may be employed. A taperedsurface or feature configuration may improve positioning of the blank inrelation to the shank, and also may eliminate conventional machining ofthreads therebetween. Exemplary tapered, complementary surfaces that maybe easily formed for implementation of the present invention includewithout limitation surfaces of revolution such as frustoconicalsurfaces, wherein such surfaces of revolution may be formed bymachining.

In addition, a multi-pass weld procedure may be employed whereinmultiple individual circumferential welds originate from differentcircumferential positions. Such a weld procedure and configuration mayalign or maintain alignment of the welded assembly of the shank with thebit body by equalizing or minimizing distortion caused by conventionalwelding processes. Put another way, a multi-pass weld may be formedwherein subsequent weld origination circumferential positions are offsetfrom immediately preceding weld origination circumferential positions.

For instance, a first weld may originate at a first position and extendaround the circumference of a weld recess to a second position. A secondweld may then be formed that originates from a substantially differentcircumferential position than the circumferential beginning point of thefirst weld. Subsequent welds, similarly, may be formed so that eachsubsequent weld originates at a circumferential position that differsfrom its preceding weld's originating position. In one embodiment, theoriginating position for a subsequent weld may be separated from thecircumferential origination position of its preceding weld by betweenabout 90° and about 18° degrees.

It is specifically contemplated that the blank and shank configurationaccording to the present invention may be applied to coring bits,bi-center bits, eccentric bits, reaming tools and other drillingstructures as well as to full-bore drill bits. As used herein, the term“bit” encompasses all of the foregoing drilling structures, whethersteel or matrix-type. Moreover, the present invention is not limited toany particular structure for steel or matrix-type rotary drag bits andmay be applied to rotary drag bits fabricated by various methods. It isfurther contemplated that the blank and shank configuration according tothe present invention may be applied to fabrication of roller cone bits,and the term “bit” as used herein encompasses such assemblies.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a perspective view of a conventional matrix-type rotary dragbit;

FIG. 1B is a partial schematic side cross-sectional view of theconventional matrix-type rotary drag bit shown in FIG. 1A;

FIG. 1C is a partial side cross-sectional view of the shank and bit bodyof a conventional matrix-type rotary drag bit;

FIG. 1D is a side cross-sectional view of a conventional steel bodyrotary drill bit;

FIG. 2A is a partial side cross-sectional view of the shank and rotarydrill bit body of the present invention;

FIG. 2B is a partial side cross-sectional view as well as a partial sideview of a shank and bit body of the present invention;

FIGS. 2C-2D illustrate schematic top views of the multiple-pass weld andwelding process of the present invention;

FIGS. 3A-3G are partial schematic side cross-sectional views ofdifferent embodiments of interface configurations between a bit body anda shank of the present invention;

FIG. 4 is a side view of a rotary drill bit according to the presentinvention;

FIG. 5A shows a perspective view of a rotary drill bit of the presentinvention; and

FIG. 5B shows a partial top cross-sectional view of the shank and bitbody as shown in FIG. 5A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2A depicts a partial cross-sectional view of matrix-type rotarydrag bit 110 according to the present invention. Rotary drag bit 110includes central longitudinal axis 103 about which bore 112 is generallydisposed. Shank 116 may be comprised of a material having a carbonequivalent of less than about 0.35%, such as, for example and not by wayof limitation, an AISI 4130 steel or AISI 4130MOD steel and may includea threaded pin connection 117, as known in the art, for connection to adrill string (not shown) as well as a bit breaker surface 121 forassembly and disassembly thereto and therefrom, respectively. It may bedesirable for the shank material to have a carbon equivalent of evenless than about 00.35% such as, for example, less than about 0.30%. Itwill also be appreciated by those of ordinary skill in the art that thematerial selected for shank 116 exhibit, for example, at least a minimumyield strength, a minimum ultimate tensile strength and a minimum impactstrength suitable for conditions encountered during drilling with rotarydrag bit 110. The aforementioned AISI 4130 and AISI 4130 MOD steelspossess such desirable mechanical properties.

Generally, a carbon equivalent is an empirical value in weight percentthat relates the combined effects of different alloying elements used inthe making of metal alloys, such as steels, to an equivalent amount ofcarbon, as an indication of weldability or susceptibility to weldcracking. A carbon equivalent may be used for hardenable carbon andalloy steels, without limitation. Further, as seen from the followingequation, it is not necessary that the material include carbon to have anon-zero carbon equivalent. Different formulas for computing a carbonequivalent of a material, as known in the art, have been developed. Thepresent invention contemplates use of different empirical formulas forcomputation of a carbon equivalent. For example, one formula for acarbon equivalent of a given material, provided from the MetalsHandbook®, Desk Edition, published by The American Society for Metals,eighth printing May, 1995, is given below.${CE} = {{\% C} + \frac{{\%{Cr}} + {\%{Mo}} + {\% V}}{5} + \frac{{\%{Si}} + {\%{Ni}} + {\%{Cu}}}{15}}$Where:

-   CE is the carbon equivalent in weight percent;-   % C is the weight percent of carbon in the material;-   % Cr is the weight percent of chromium in the material;-   % Mo is the weight percent of molybdenum in the material;-   % V is the weight percent of vanadium in the material;-   % Si is the weight percent of silicon in the material;-   % Ni is the weight percent of nickel in the material; and-   % Cu is the weight percent of copper in the material.    Thus, it will be appreciated that a material possessing desired    mechanical properties for use in shank 116 may be readily qualified    in terms of carbon equivalvent as to its suitability for use in    implementation of the present invention.

In addition, shank 116 may also include tapered surface 160 configuredto matingly engage complementary tapered surface 161 of bit body 123,thus positioning shank 116 with respect to bit body 123 and forming, incombination with tapered surface 141 of bit body 123, weld recess 139.By way of example only, and as applicable to this and the otherillustrated embodiments of the present invention, the referenced taperedsurfaces may, but do not necessarily have to be, implemented asfrustoconical surfaces. Vertical surface 150 of shank 116 may extendwithin bit body 123 along vertical surface 151 of bit body 123, but maybe configured with tapered surface 160 to position shank 116 withrespect to bit body 123. FIG. 2A also shows that horizontal surface 140radially inward of tapered surface 160 may be separated from horizontalsurface 152 of bit body 123 by gap 111 to prevent contact therebetween,because such contact may affect position of shank 116 in relation to bitbody 123, notwithstanding mutual contact of tapered surface 160 andtapered surface 161. As note above, radially outermost portions oftapered surface 160 and tapered surface 161 together definecircumferential weld recess 139 wherein a weld 170, such as a multi-passweld according to the present invention, may be formed.

FIG. 2B shows a partial side cross-sectional view of a rotary drill bit310 (left-hand side of figure) and a partial side view of rotary drillbit 310 about its longitudinal axis 333 (right-hand side of figure)prior to welding in accordance with the present invention. Rotary drillbit 310 may generally comprise a bit body 323 including a plurality oflongitudinally extending blades 314 defining junk slots 316therebetween. Each blade 314 may define a leading or cutting face 318that extends radially along the bit face around the distal end 315 ofthe rotary drill bit 310, and may include a plurality of cutting elementpockets 319 formed within bit body 323 and oriented for affixing cuttingelements 320 therein to cut a subterranean formation upon rotation ofthe rotary drill bit 310. Cutting elements 320 are shown forillustration only, as they may be affixed to the cutting element pockets319 after the shank 334 is welded to the bit body 323. Shank 334,according to the present invention, may comprise a material having acarbon equivalent of less than about 0.35%, such as an AISI 4130 or AISI4130MOD steel. Each blade 314 may include a longitudinally extendinggage portion 322 that corresponds to the gage 312 of each blade 314,sized according to approximately the largest-diameter-portion of therotary drill bit 310 and thus may be typically only slightly smallerthan the diameter of the hole to be drilled by rotary drill bit 310. Theupper longitudinal end 317 of the rotary drill bit 310 includes athreaded portion or pin 325 to threadedly attach the rotary drill bit310 to a drill collar or downhole motor, as is known in the art. Inaddition, the plenum 329 or bore longitudinally extends within rotarydrill bit 310 for communicating drilling fluid therewithin throughnozzles 336 disposed on the face of the rotary drill bit 310 throughpassages (not shown extending from plenum 329 to nozzles 336. Threadedportion 325 may be machined directly into the upper longitudinal end 317of the shank 334 as may bit breaker surface 321 for loosening andtightening the tapered threaded portion 325 of the rotary drill bit 310when installed into the drill string, the shank 334 engaging the bitbody 323 of the rotary drill bit 310 at its distal end as depicted inthe cross-sectional view thereof.

Also as shown in FIG. 2B, the tapered surface 350 of the shank 334 maymatingly engage the tapered surface 351 of the bit body 323 in order toposition the shank 334 in relation to the bit body 323. Of course,vertical surface 360 of shank 334 may engage vertical surface 361(vertical surfaces 360 and 361 not necessarily being threaded asdepicted in FIG. 2B) and horizontal surface 360 of shank 334 may or maynot engage horizontal surface 371 according to actual clearancestherebetween, the desirability of a gap being heretofore described withrespect to FIG. 2A. Weld recess 339 may be formed by tapered surface 350of shank 334 and tapered surface 352 of the bit body 323.

A multi-pass weld of the present invention, as described hereinbelow,may be formed and disposed generally within weld recess 339. As notedabove, shank 334 may comprise a material having a carbon equivalent ofless than about 0.35%, such as, for example, an AISI 4130, an AISI4130MOD steel, or an equivalent material. Therefore, preheating shank334 prior to initiating the welding process may not be necessary. As afurther advantage, aligning the shank 334 with respect to the bit body323 and then tack-welding the assembly together may be accomplished.FIG. 2C shows a schematic top cross-sectional view of multi-pass weld401 of the present invention in relation to the inner apex or tip 340 ofthe weld recess 339 as shown in FIG. 2B. More particularly, FIG. 2Cshows a top view of the inner boundary of weld recess 339 as defined bytip 340 thereof as well as welds 410, 420, 430, and 440. Welds 410, 420,430, and 440 are depicted as concentric rings or circles of increasingdiameter and are shown as being separate from one another. However, FIG.2C is merely schematic, and welds 410,420, 430, and 440 are depicted asshown merely for clarity. Welds 410, 420, 430, and 440 may be disposedanywhere generally within weld recess 339, depending on the size of theprevious welding passes and the size of the welding recess 339. Ofcourse, the longitudinal position of any weld of the present inventionmay be varied in order to fill the weld recess relatively evenly.

As shown in FIG.2C, a first weld 410 or “root” weld may be depositedwithin the weld recess 339, or more specifically, positioned along thecircumference of tip 340 of the weld recess 339 formed by the interfacebetween the facing surfaces 350 and 352 of the shank 334 and the bitbody 323. First weld 410 may extend around the circumference of tip 340of weld recess 339. First weld 410, as shown in FIG. 2C, may originateat circumferential position 409 and may also terminate thereat.Alternatively, first weld 410 may originate at a first circumferentialposition and may terminate at a second circumferential position. Secondweld 420, as shown in FIG. 2C, may originate at circumferential position419 and may terminate thereat. Alternatively, second weld 420 mayoriginate at a first circumferential position separated from thecircumferential origination position of the first weld 410 by at leastabout 90° and may terminate at a second circumferential position.

Therefore, circumferential position 409 may be separated fromcircumferential position 419 by at least about 90°, measured in relationto the longitudinal axis 333 of drill bit 310, either in the clockwiseor counter-clockwise direction. Separation angle θ, shown by FIG. 2C,illustrates such a measure of separation between circumferentialposition 409 and circumferential position 419. Further, second weld 420may originate at a first circumferential position separated from theoriginating circumferential position of the immediately preceding weldby at least about 90°, and may terminate at a second circumferentialposition. In addition, second weld 420 may be formed about longitudinalaxis 333 in a circumferential direction (clockwise or counter-clockwise)opposite to or consistent with the direction that the initial weld 410was formed.

Third weld 430, as shown in FIG. 2C, originates at circumferentialposition 429 and also terminates thereat. More generally, third weld 430may originate at a first circumferential position separated from theoriginating circumferential position of the immediately preceding weldby at least about 90°, and may terminate at a second circumferentialposition. Fourth weld 440, as shown in FIG. 2C, originates atcircumferential position 439 and also terminates thereat. Similarly,fourth weld 440 may originate at a first circumferential positionseparated from the originating circumferential position of theimmediately preceding third weld 430 by at least about 90°, and mayterminate at a second circumferential position. As may also be seen fromFIG. 2C, circumferential originating positions 409, 419, 429, and 439may be substantially symmetrically distributed about the circumferenceof tip 340 of weld recess 339.

Of course, the separation between an originating position of a precedingweld and the originating position of a subsequent weld may be measuredin relation to the circumferential distance therebetween. For instance,the circumferential separation distance between circumferential position409 and circumferential position 419 may be at least about one quarterof the circumference of the circle depicting weld recess tip 340.

Therefore, a multi-pass weld of the present invention may include aninitial weld originating at a first circumferential position andterminating at a second circumferential position and a second weldoriginating at a circumferential position at least about 90° from thefirst position of the first weld or at least about one quarter of thecircumference of the tip 340 of weld recess 339. Subsequent welds mayoriginate at respective circumferential positions that are separated byat least about 90° from the circumferential originating position oftheir immediately preceding weld or a distance of at least about onequarter of the circumference of the tip 340 of weld recess 339,therearound, respectively. Circumferential positions may only beseparated by up to 180°, since such positioning would be on oppositesides of a line from one edge of the circumference through the centerthereof to the other side of the circumference. Thus, subsequent weldsmay originate at respective circumferential positions that are separatedfrom the originating position of the immediately preceding weld by about90° to 180° from the originating position of the immediately precedingweld in accordance with the present invention. Such a weld configurationmay reduce, equalize, or minimize distortion and misalignment betweenthe assembled shank 334 and bit body 323.

As a further example of the multi-pass weld of the present invention,and without limitation, FIG. 2D shows a top cross-sectional view ofmulti-pass weld 402 in relation to the tip 340 of the weld recess 339 asshown in FIG. 2B. Welds 452, 454, 456, 458, 460, and 462 may be formedand extend around the circumference of the tip 340 of weld recess 339.First weld 452 may originate at circumferential position 453 and mayalso terminate thereat. Second weld 454 may originate at circumferentialposition 455 and may also terminate thereat. Third weld 456, mayoriginate at circumferential position 457 and may also terminatethereat. Fourth weld 458, may originate at circumferential position 459and may also terminate thereat. Fifth weld 460, may originate atcircumferential position 461 and may also terminate thereat. Sixth weld462, may originate at circumferential position 463 and may alsoterminate thereat.

Alternatively, and more generally, each weld 452, 454, 456, 458, 460,and 462 may originate at a first circumferential position that is offsetfrom or separated from the circumferential origination position of itspreceding weld. Thus, subsequent welds 454, 456, 458, 460, and 462,meaning welds that occur after a preceding weld, may originate at acircumferential position separated from the originating circumferentialposition of the immediately preceding weld by at least about 90° or atleast about one quarter of the circumference of weld tip 340. Forinstance, separation angle θ, shown by FIG. 2D, illustrates a measure ofseparation between circumferential position 459 and circumferentialposition 463 of about 120°. Put another way, the separation distancebetween circumferential position 459 and circumferential position 463 asshown in FIG. 2D is about one third of the circumference of the circledepicting weld recess tip 340. Further, welds 452, 454, 456, 458, 460,and 462 may be formed about longitudinal axis 333 along anycircumferential direction (clockwise or counter-clockwise).

Thus, the multi-pass weld of the present invention is not limited to anyparticular number of discrete welds, but rather comprises more than oneweld wherein the origination position of a preceding and subsequent weldis separated by at least about 90° or at least about one quarter of thecircumference of the weld recess tip. Further, the welds may or may notextend circumferentially or at all. For instance, the welds may beformed by applying a heat source and welding medium at a particularposition, forming a weld and then positioning the heat source andwelding medium at a second position and forming another weld. Thus,welds may be formed within a weld recess at discrete locations. Inaddition, the separation between the circumferential position oforigination between a preceding and immediately subsequent weld mayvary. For instance, the separation angle θ may be about 90°, then about135°, then about 180°, for the second weld, the third weld, and thefourth weld, respectively, without limitation. Further, the originationpositions of the welds may form a substantially symmetrical pattern, ormay form an unsymmetrical pattern.

FIG. 3A shows a partial cross-sectional view of an interface 200 betweena shank 216 and a bit body 223 with respect to bore 212 centered aboutcentral axis 203 of a rotary drag bit (remainder not shown). Shank 216may comprise a material having a carbon equivalent of less than about0.35% and may include tapered surface 260, tapered surface 250, andhorizontal surface 253. Tapered surface 250 of shank 216 may beconfigured to matingly engage tapered surface 251 of bit body 223 toposition shank 216 with respect to bit body 223. Further, gap 211 mayseparate horizontal surface 253 of shank 216 and horizontal surface 252of bit body 223, thus inhibiting engagement therebetween that may affectthe proper mating engagement between tapered surface 250 of shank 216and tapered surface 251 of bit body 223. Weld recess 239 may be formedby the intersection of tapered surface 260 of shank 216 with taperedsurface 241 of bit body 223. As may be further seen in FIG. 3A, taperedsurface 251 and horizontal surface 252 of bit body 223 may form a cavitywhich the lower longitudinal end of shank 216 fits within. Such aconfiguration may be advantageous for distributing stresses transmittedthrough the shank 216 during operation of the rotary drag bit.

Alternatively, gap 211 may be reduced or eliminated by way of alongitudinal force applied to compress the bit body 223 and the shank216 against one another. Stated another way, it may be desirable toconfigure tapered surface 250 of shank 216 and tapered surface 251 ofbit body 223 so that a sufficient compressive force causes slidingtherebetween, reducing gap 211 or causing horizontal surface 253 ofshank 216 to engage horizontal surface 252 of bit body 223. Such acompressive force may be applied prior to or during welding of the shank216 to the bit body 223, or both, and may be desirable as generating atensile residual stress within the multi-pass weld (FIG. 2C and 2D) thatmay be counter-acted by the compressive forces experienced duringdrilling. Such a configuration may reduce the stresses in the weldduring drilling. As a further alternative, gap 211 may be eliminated bysizing the shank and bit body accordingly.

FIG. 3B shows a partial cross-sectional view of another embodiment ofinterface 201 between shank 216 and bit body 223 with respect to bore212 centered about central axis 203 of a rotary drag bit (remainder notshown). Shank 216 may comprise a material having a carbon equivalent ofless than about 0.35%, such as, for example, an AISI 4130 or AISI4130MOD steel and may include tapered surface 260, tapered surface 250,and horizontal surface 253. Tapered surfaces 250 and 260 of shank 216may be configured to matingly engage tapered surfaces 251 and 261 of bitbody 223, respectively, to position shank 216 with respect to bit body223. Such a dual-taper configuration may be advantageous for positioningthe shank 216 with respect to the bit body 223.

Further, gap 211 may separate horizontal surface 253 of shank 216 andhorizontal surface 252 of bit body 223, thus inhibiting engagementtherebetween that may affect the proper mating engagement betweentapered surfaces 250 and 260 of shank 216 and tapered surfaces 251 and261 of bit body 223, respectively. Weld recess 239 may be formed by theengagement of tapered surface 260 of shank 216 with tapered surface 241of bit body 223. As may be further seen in FIG. 3B, tapered surface 251and horizontal surface 252 of bit body 223 may form a cavity which thelower longitudinal end of shank 216 fits within. Such a configurationmay be advantageous for distributing stresses transmitted through theshank 216 during operation of the rotary drag bit (not shown).

FIG. 3C shows a partial cross-sectional view of another embodiment ofthe present invention depicting interface 202 between shank 216 and bitbody 223 with respect to bore 212 centered about central axis 212 of arotary drag bit (not shown). As shown in FIG. 3C, tapered surface 270 ofshank 216 may be sloped longitudinally downward along a radially inwardpath, and may matingly engage tapered surface 271 of bit body 223, whichmay slope longitudinally upward along a radially outward path. Thus,mating engagement between tapered surface 270 of shank 216 and taperedsurface 271 of bit body 223 may position shank 216 with respect to bitbody 223. Weld gap 239 may be substantially formed by the intersectionof tapered surface 241 of bit body 223 and tapered surface 270 of shank216. Of course, chamfers and radii at boundaries between adjacentsurfaces may be used in accordance with engineering design to facilitateproper engagement between tapered surface 270 of shank 216 and taperedsurface 271 of bit body 223. As may also be seen in reference to FIG.3C, tapered surface 271 of bit body 223 may form a cavity which thelower longitudinal portion of shank 216 fits within. Such aconfiguration may be advantageous for distributing stresses duringoperation of the rotary drag bit (not shown). In addition, shank 216 maycomprise a material having a carbon equivalent of less than about 0.35%,in order to eliminate the need for preheating prior to welding of theshank 216 to the bit body 223.

FIG. 3D shows a partial cross-sectional view of yet another embodimentof the present invention depicting interface 204 between shank 216 andbit body 223 with respect to bore 203 centered about central axis 212 ofa rotary drag bit (remainder not shown). As shown in FIG. 3D, taperedsurface 280 of shank 216 may slope longitudinally upward along aradially inward path, and may matingly engage tapered surface 281 of bitbody 223, which may slope longitudinally downward along a radiallyoutward path. Thus, mating engagement between tapered surface 280 ofshank 216 and tapered surface 281 of bit body 223 may position shank 216with respect to bit body 223.

Weld gap 239 may be substantially formed by the intersection of taperedsurface 282 of bit body 223 and tapered surface 280 of shank 216. Shank216 may comprise a material having a carbon equivalent of less thanabout 0.35%, such as, for example, an AISI 4130 steel, an AISI 4130MODsteel, or an equivalent material to eliminate the need for preheatingthe shank prior to welding the shank 216 and bit body 223 to oneanother. Such a configuration may allow the shank 216 and bit body 223to be tack welded in order to maintain the relative positioning thereofprior to forming the multi-pass weld as described above and eliminateconventional preheating thereof during welding.

FIG. 3E shows a further embodiment of the present invention depicting across-sectional view of interface 205 between shank 216 and bit body223. As mentioned above, shank 216 may comprise a material having acarbon equivalent of less than about 0.35%. Shank 216 and bit body 223are shown in relation to bore 203, which is centered about central axis212 of a rotary drag bit (remainder not shown). Tapered surface 292 ofshank 216 may matingly engage tapered surface 293 of bit body 223 toposition the shank 216 in relation to the bit body 223. Also, horizontalsurface 300 of shank 216 may matingly engage horizontal surface 295 ofbit body 223, thereby vertically positioning the shank 216 in relationto the bit body 223. Gap 299 may exist between tapered surface 290 ofshank 216 and tapered surface 297 of bit body 223. Gap 299 may provideclearance for fitting the shank 216 and the bit body 223 together. Weldrecess 239 may be substantially formed by tapered surface 290 of shank216 and tapered surface 291 of bit body 223.

FIGS. 3F and 3G show a cross-sectional view of interface 206 accordingto the present invention between shank 216 and bit body 223. Morespecifically, a deformable element 302 may be positioned between shank216 and bit body 223. As shown in FIG. 3F and 3G, deformable element 302may be positioned between horizontal surface 304 of shank 216 andhorizontal surface 305 of bit body 223. Gap 311 may exist initiallybetween tapered surface 306 of shank 216 and tapered surface 307 of bitbody 223. Further, tapered surface 303 of bit body 223 may engagetapered surface 308 of shank 216 or, alternatively, there may be slightclearance therebetween. However, as shown in FIG. 3G, shank 216 may bedisplaced so as to deform deformable element 302 and position taperedsurface 306 of shank 216 to matingly engage tapered surface 307 of bitbody 223, thus substantially eliminating gap 311. Such a configurationmay be preferable to position the shank 216 in relation to the bit body223 by way of a compressive force. Such a compressive force may beapplied prior to and/or during welding of the shank 216 to the bit body223, and may effect a tensile residual stress within the multi-pass weld(FIGS. 2C and 2D) that may be desirable as reducing the stresses in theweld during drilling. Also, as shown in FIGS. 3F and 3G, weld recess 339may be substantially formed by tapered surface 306 of shank 216 andtapered surface 301 of bit body 223. Exemplary deformable elements 302include high temperature elastomeric rings, annular leaf springs andBelleville springs, as well as nonresilient deformable materials thatmay be crushed as gap 311 is eliminated. Deformation, resilient ornonresilient, of deformable element 302 may provide controlled downwardmovement of shank 216 as it is caused to engage bit body 223.

FIG. 4 shows an exemplary rotary drag bit 500 according to the presentinvention wherein an interface and multi-pass weld as described abovehave been completed to affix bit body 323, either steel body ormatrix-type, to the shank 334. Shank 334 may include bit breakersurfaces or flats 321 for loosening and tightening the tapered threadedportion 325 of the rotary drag bit 500 when installed into the drillstring. Rotary drag bit 500 may include radially and longitudinallyextending blades 314, wherein each blade 314 may define a leading orcutting face 318 and may include a plurality of cutting elements 320affixed thereto and oriented therein to cut a subterranean formationupon rotation of the rotary drill bit 500. Nozzles 336 may be sized andpositioned to communicate drilling fluid from the interior of the rotarydrag bit 500 to the cutting elements 320 and blades 314 to cleancuttings therefrom. Upon completion of multi-pass weld (not shown), theexterior, radially outward surface thereof may be machined flush with anouter surface of bit body 323. Further, it should be understood that thepresent invention is not limited to rotary drill bits fabricated by wayof any particular method; rather, the present invention may be practicedwith rotary drill bits fabricated by any method.

Generally, the tapered surface arrangements and configurations of thepresent invention may provide an efficient mechanism to position theshank in relation to the bit body in preparation for weldingtherebetween. In addition, a longitudinal, generally axial force may beapplied to the shank or bit body as described hereinabove to facilitatepositioning or centering of the shank in relation to the bit body, withor without the disposition of a deformable element therebetween. Also, alongitudinal force may be applied to achieve a desired stress state inthe assembly in relation to welding the shank to the bit body. Thelongitudinal force may be applied externally, by way of a piston or byother force generation means. On the other hand, with respect only topositioning, the tapered surfaces of the shank and bit body may beconfigured and sized so that the weight of the shank as it is disposedlongitudinally above the bit body facilitates positioning or centeringthereof in relation to the bit body as it is lowered thereonto. In sucha configuration, the shank may be “self-centering.”

In addition, although the foregoing descriptions depict “taperedsurfaces” in the form of cross-sectional representations that may implycontinuous annular surfaces such as frustoconical surfaces, the presentinvention contemplates that the tapered surfaces may comprise moregenerally tapered features that may or may not be continuous and may ormay not be linear in cross-section. Likewise, although the foregoingillustrations and descriptions may imply an annular weld recess, manyalternatives are contemplated by the present invention. For instance,the multi-pass weld of the present invention may be formed in relationto, generally, a region configured for forming a welded connectionbetween the shank and bit body, without limitation.

More specifically, the present invention contemplates that complementarylongitudinal recesses may be formed in the mating ends of both the shankand bit body for welding to one another. In other words, thelongitudinal mating ends of both the shank and bit body may comprisesplines that may be aligned to form longitudinal weld recesses. In sucha configuration, a respective weld may be formed within each alignedlongitudinal weld recess. However, in such a configuration, themulti-pass weld of the present invention may be formed within thelongitudinal weld recesses. More specifically, in such a configuration,a first weld may originate from a first circumferential position and asecond weld may originate from a circumferential position separated fromthe first circumferential position. Each subsequent weld may originatefrom a respective circumferential position that is at least about 90°from the origination position of its immediately preceding weld.

FIG. 5A shows a perspective view of a rotary drill bit 610 prior towelding in accordance with the present invention. Rotary drill bit 610may generally comprise a bit body 623 including a plurality oflongitudinally extending blades 614 defining junk slots 616 therebetweenand having a leading or cutting face 618 that extends radially along thebit face of the rotary drill bit 610. Bit body 623 may include aplurality of cutting elements 620 affixed thereto to cut a subterraneanformation upon rotation of the rotary drill bit 610. Cutting elements620 are shown for illustration only, as they may be affixed to the bitbody 623 after the shank 634 is welded to the bit body 623, inaccordance with conventional practices. Shank 634, according to thepresent invention, may comprise a material having a carbon equivalent ofless than about 0.35%. For example, an AISI 4130 steel, an AISI 4130MODsteel, or any material having a carbon equivalent of less than about0.35% may be used, without limitation. Each blade 614 may define alongitudinally extending gage portion 622 that corresponds to the gage612 of each blade 614, sized according to approximately thelargest-diameter-portion of the rotary drill bit 610. The upperlongitudinal end 617 of the rotary drill bit 610 includes a threadedportion or pin 625 to threadedly attach the rotary drill bit 610 to adrill string, as is known in the art. In addition, drilling fluid may becommunicated through nozzles 636 disposed on the face of the rotary dragbit 610.

Shank 634 includes longitudinal recesses 650 which correspond tolongitudinal recesses 660 of bit body 623. Further, shank 634 mayinclude tapered feature 670, which may be configured according to any ofthe embodiments described in FIGS. 2A, 2B, and 3A-3G, and which may betermed a protrusion for the sake of convenience only. Of course, bitbody 623 may include a complementary tapered feature (not shown), whichmay be termed a recess for the sake of convenience only. Upon assemblyof shank 634 and bit body 623, the longitudinal recesses 650 of theshank 634 and the longitudinal recesses 660 of the bit body 623 may bealigned circumferentially. FIG. 5B shows a partial top cross-sectionalview of the longitudinal recesses 650 of the shank 634 and thelongitudinal recesses 660 of the bit body 623 wherein the longitudinalrecesses 650 and 660 are vertically superimposed and circumferentiallyaligned. Such alignment may form weld recesses 655, as shown in FIG. 5B.

Further, according to the present invention, a multi-pass weld may beformed within weld recesses 655. A first weld 680 is shown in FIG. 5B ata circumferential position of origination 682, and may extendlongitudinally within the aligned longitudinal recesses 650 and 660. Asecond weld 681 may be formed at a circumferential position oforigination 683 that is separated from the circumferential position oforigination 682 of first weld 680 by at least 90°, as depicted byseparation angle θ in relation to longitudinal axis 661. Subsequentwelds (not shown) may be positioned so that each subsequentcircumferential position of origination is separated from thecircumferential position of origination of its immediately precedingweld.

There are many alternative implementation that are contemplated andencompassed by the present invention. For instance, a weld region may beformed by alignment of spiraled splines or recesses in one or both ofthe shank and bit body. Further, although the multi-pass weld of thepresent invention may be described in terms of preceding and subsequentwelds, as hereinabove, it is contemplated that one or more welds of thepresent invention may be formed substantially simultaneously by way ofapplication of multiple heat sources and disposition of weldingmaterials at more than one location within a weld region. In such aconfiguration, a simultaneously formed weld may be taken as eithersubsequent or preceding in relation to any other weld simultaneouslyformed therewith, without limitation. For example, without limitation,the present invention contemplates that two welds may be formedsubstantially simultaneously, separated by a separation angle of atleast about 90°. Further, for example, without limitation, the presentinvention contemplates that three welds may be formed substantiallysimultaneously, wherein at least two of the three welds are separated byat least about 90°. Such a configuration may increase the cost of thewelding equipment, but may also increase the speed or performance of thewelding process and further reduce any tendency toward misalignment ofthe shank and bit body that may be induced by welding.

While the present invention has been described herein with respect tocertain preferred embodiments, those of ordinary skill in the art willrecognize and appreciate that it is not so limited. Rather, manyadditions, deletions and modifications to the preferred embodiments maybe made without departing from the scope of the invention as hereinafterclaimed. In addition, features from one embodiment may be combined withfeatures of another embodiment while still being encompassed within thescope of the invention as contemplated by the inventors. Further, theinvention has utility in drill bits and core bits having different andvarious bit profiles as well as cutter types.

1. A rotary drill bit for drilling a subterranean formation, comprising:a bit body having a centerline and including a leading end forcontacting a formation during drilling; a shank structure, comprising:at least one tapered feature matingly engaging at least onecomplementary tapered feature of the bit body and at least in partpositioning the shank structure in relation to the bit body; and atrailing end having structure associated therewith for connecting therotary drill bit to a drill string; a weld region substantially formedby at least one surface of the shank structure and at least one surfaceof the bit body; a multi-pass weld affixing the shank structure to thebit body substantially disposed within the weld region, comprising: afirst plurality of welds comprising: a first weld originating from afirst circumferential position; and a second weld originating from asecond circumferential position; wherein the second circumferentialposition and the first circumferential position are separated by atleast about 90° in relation to the centerline of the bit body; and atleast one cutting element secured to the bit body.
 2. The rotary drillbit of claim 1, wherein the shank structure comprises a material havinga carbon equivalent of less than about 0.35%.
 3. The rotary drill bit ofclaim 2, wherein the shank structure comprises AISI 4130 steel or AISI4130MOD steel.
 4. The rotary drill bit of claim 1, wherein the first andsecond welds are formed substantially simultaneously.
 5. The rotarydrill bit of claim 1, wherein the multi-pass weld exhibits a stressstate at least in part responsive to a force applied between the atleast one tapered feature of the shank structure and the at least onecomplementary feature of the bit body during formation of the multi-passweld.
 6. The rotary drill bit of claim 1, wherein the weld regioncomprises a substantially annular groove.
 7. The rotary drill bit ofclaim 6, wherein the first weld and second weld extendcircumferentially.
 8. The rotary drill bit of claim 1, wherein the weldregion comprises a plurality of weld recesses formed by circumferentialalignment of longitudinal recesses of the shank structure andlongitudinal recesses of the bit body.
 9. The rotary drill bit of claim8, wherein the first weld and the second weld extend longitudinallywithin respective, circumferentially aligned longitudinal recesses ofthe shank structure and the bit body.
 10. The rotary drill bit of claim1, wherein a portion of the shank structure is disposed within a cavityformed within the bit body.
 11. The rotary drill bit of claim 10,wherein the at least one complementary feature of the bit body forms atleast a portion of the cavity.
 12. The rotary drill bit of claim 1,further comprising at least one other weld, wherein a circumferentialposition of origination of the at least one other weld is separated byat least about 90° from the second circumferential position of thesecond weld.
 13. The rotary drill bit of claim 12, wherein the at leastone other weld comprises a second plurality of welds; wherein each ofthe second plurality of welds includes a circumferential position oforigination, respectively; and wherein the circumferential position oforigination of each of the second plurality of welds is separated from acircumferential position of origination of its immediately precedingweld by at least 90°.
 14. The rotary drill bit of claim 13, wherein thecircumferential positions of origination of the welds of the firstplurality of welds and the circumferential positions of origination ofthe welds of the second plurality of welds are positioned substantiallysymmetrically in relation to a circumference of the weld region.
 15. Therotary drill bit of claim 1, further comprising a deformable elementdisposed between the shank structure and the bit body.
 16. The rotarydrill bit of claim 15, wherein the deformable element exhibitscompressive stress generated between one or more surfaces of the shankstructure and one or more surfaces of the bit body.
 17. The rotary drillbit of claim 15, wherein the deformable element is deformed by acompressive stress generated between one or more surfaces of the shankstructure and one or more surfaces of the bit body.
 18. The rotary drillbit of claim 15, wherein the multi-pass weld exhibits a stress state atleast in part responsive to a stress generated between one or moresurfaces of the shank structure and one or more surfaces of the bitbody.
 19. The rotary drill bit of claim 1, wherein the at least onetapered feature of the shank structure comprises a tapered surface. 20.The rotary drill bit of claim 19, wherein the at least one complementaryfeature of the bit body comprises a tapered surface.
 21. The rotarydrill bit of claim 20, wherein the at least one complementary feature ofthe bit body forms a cavity therein.
 22. The rotary drill bit of claim21, wherein a portion of the shank structure is disposed within thecavity formed within the bit body.
 23. The rotary drill bit of claim 22,wherein the weld region comprises a substantially annular groove. 24.The rotary drill bit of claim 23, further comprising at least one otherweld, wherein a circumferential position of origination of the at leastone other weld is separated by at least about 90° from the secondcircumferential position of the second weld.
 25. The rotary drill bit ofclaim 24, wherein the at least one other weld comprises a secondplurality of welds; wherein each of the second plurality of weldsincludes a circumferential position of origination, respectively; andwherein the circumferential position of origination of each of thesecond plurality of welds is separated from a circumferential positionof origination of its immediately preceding weld by at least 90°. 26.The rotary drill bit of claim 25, wherein each of the first plurality ofwelds and each of the second plurality of welds extendscircumferentially.
 27. The rotary drill bit of claim 25, wherein each ofthe first plurality of welds and each of the second plurality of weldsextends substantially around an entire circumference of the weld groove.28. The rotary drill bit of claim 1, wherein the at least one cuttingelement comprises a polycrystalline diamond compact.
 29. A rotary drillbit for drilling a subterranean formation, comprising: a bit body havinga centerline and including a leading end for contacting a formationduring drilling; a shank structure, comprising: at least one taperedfeature matingly engaging a complementary feature of the bit body and atleast in part positioning the shank structure in relation to the bitbody; and a trailing end having structure associated therewith forconnecting the rotary drill bit to a drill string; a weld recesssubstantially formed by at least one surface of the shank structure andat least one surface of the bit body; a multi-pass weld affixing theshank structure to the bit body substantially disposed within the weldrecess, comprising: a first weld originating from a firstcircumferential position and having an associated circumferentialextent; and a second weld originating from a second circumferentialposition and having an associated circumferential extent; wherein thesecond circumferential position and the first circumferential positionare separated by a distance of at least about one quarter of theassociated circumference of the first circumferential position; and atleast one cutting element secured to the bit body.
 30. A method offabricating a rotary drill bit, comprising: providing a shank structurefor attaching the rotary drill bit to a drill string configured with atleast one tapered feature for positioning the shank structure; providinga bit body having an end configured for drilling a subterraneanformation, the bit body including at least one complementary taperedfeature for positioning the shank structure in relation thereto;positioning the shank structure by matingly engaging the at least onetapered feature of the shank structure and the at least onecomplementary tapered feature of the bit body and defining a weld regionbetween the shank structure and the bit body; forming a first weldoriginating from a first circumferential position within the weldregion; forming at least a second weld originating from a secondcircumferential position within the weld region; wherein the secondcircumferential position and the first circumferential position areseparated by at least about 90° in relation to the centerline of the bitbody.
 31. The method of fabricating a rotary drill bit of claim 30,wherein providing the shank structure comprises providing a shankstructure formed from a material having a carbon equivalent less thanabout 0.35%.
 32. The method of fabricating a rotary drill bit of claim31, wherein providing a shank structure formed from a material having acarbon equivalent less than about 0.35% comprises providing a shankstructure formed from AISI 4130 steel or AISI 4130MOD steel.
 33. Themethod of fabricating a rotary drill bit of claim 30, wherein formingthe first weld and forming the at least a second weld comprises formingthe first weld and the at least a second weld substantiallysimultaneously.
 34. The method of fabricating a rotary drill bit ofclaim 30, further comprising applying a compressive force between the atleast one tapered feature of the shank structure and the at least onecomplementary tapered feature of the bit body while forming the firstweld.
 35. The method of fabricating a rotary drill bit of claim 30,wherein providing a shank structure configured with at least one taperedfeature comprises providing a shank structure configured with at leastone tapered surface.
 36. The method of fabricating a rotary drill bit ofclaim 35, wherein providing a bit body including at least onecomplementary tapered feature comprises providing a bit body includingat least one complementary tapered surface.
 37. The method offabricating a rotary drill bit of claim 36, wherein the at least onecomplementary tapered surface of the bit body forms a cavity therein.38. The method of fabricating a rotary drill bit of claim 37, furthercomprising disposing a portion of the shank structure within the cavityformed within the bit body.
 39. The method of fabricating a rotary drillbit of claim 38, further comprising configuring the weld region to be asubstantially annular groove.
 40. The method of fabricating a rotarydrill bit of claim 38,wherein forming at least a second weld comprisesforming more than one weld, wherein each of the more than one weldincludes a circumferential position of origination, respectively; andselecting an origination position of each of the more than one weld tobe separated from the circumferential position of origination of itsimmediately preceding weld by at least about 90°.
 41. The method offabricating a rotary drill bit of claim 40, wherein forming the firstweld and each of the more than one welds comprises forming acircumferentially extending weld.
 42. The method of fabricating a rotarydrill bit of claim 41, wherein forming a circumferentially extendingweld comprises forming a weld that extends substantially around theentire circumference of the weld region.
 43. The method of fabricating arotary drill bit of claim 30, wherein positioning the shank structure bymatingly engaging the at least one tapered feature of the shankstructure and the at least one tapered complementary feature of the bitbody comprises deforming a deformable element positioned between theshank structure and the bit body.
 44. The method of fabricating a rotarydrill bit of claim 30, further comprising forming the first weld and theat least a second weld without preheating at least the shank structure.45. A method of fabricating a rotary drill bit, comprising: providing ashank structure for attaching the rotary drill bit to a drill string;providing a bit body having an end configured for drilling asubterranean formation; positioning the shank structure in contact withthe bit body and defining a weld region between the shank structure andthe bit body; and forming at least one weld within the weld region inthe absence of preheating of at least the shank structure.
 46. A rotarydrill bit for drilling a subterranean formation, comprising: a bit bodyhaving a centerline and including a leading end for contacting aformation during drilling; a shank structure, comprising at least onefrustoconical feature matingly engaging a complementary frustoconicalfeature of the bit body; a weld recess substantially formed by at leastone surface of the shank structure and at least one surface of the bitbody; at least one weld affixing the shank structure to the bit bodysubstantially disposed within the weld recess; and at least one cuttingelement secured to the bit body.
 47. A shank structure for a rotarydrill bit, comprising: at least one feature for engaging a complementaryfeature of a bit body; a trailing end having structure associatedtherewith for connecting the rotary drill bit to a drill string; andwherein the shank structure comprises a material having a carbonequivalent less than about 0.35%.